Welcome to Gil Pontius’ home page from
which you can obtain copies of the publications below. If you would like my
other publications, please see my CV, and then send your
request to me (rpontius@clarku.edu).

Robert Gilmore Pontius Jr has developed quantitative methods
that have contributed greatly to Geographic Information Science (GIS) and
Remote Sensing. Pontius began his career as an applied statistician and
environmental scientist with expertise in geographic information science (GIS),
ecological modeling, and land change science. The applied nature of his diverse
activities has inspired him to derive mathematical proofs for generally
applicable concepts concerning spatial measurements that are essential in GIS
and Remote Sensing. Several of these methods have been incorporated into the
GIS & Image Processing software Idrisi,
which has over 100,000 users worldwide.

Pontius’ most
important intellectual creation is a conceptual philosophy to compare maps
mathematically in ways that match visual intuition. One can understand the
philosophy in the context of comparison of two maps that share the same set of
categories, such as the comparison of maps of land classes from two time points
or the comparison between ground information versus a classified map. The
philosophy focuses on the disagreement between the maps because it is more
important to understand the disagreement than the agreement for practical
purposes, such as characterizing land change or improving a classifier.
Pontius’ approach separates the overall disagreement between the maps into two
components: quantity disagreement and allocation disagreement. Quantity disagreement is the amount of difference between the
reference map and a comparison map that is due to the less than perfect match
in the proportions of the categories. Allocation disagreement is the amount of
difference between the reference map and a comparison map that is due to the
less than maximum match in the spatial allocation of the categories, given the
proportions of the categories in the reference and comparison maps. It
is important to separate overall disagreement into these two components,
because these two components have different interpretations and implications
for practical applications. For example, if the purpose is to estimate change
over time in overall forest area on a landscape, then quantity disagreement is
much more important than allocation disagreement. Pontius (2000 & 2002)
were the first publications in the sequence to establish this approach, while
Pontius and Millones (2011) is the most recent and clearest articulation of
this philosophy. Pontius, Shusas, and McEachern (2004) used the philosophy to derive new
measurements to characterize transitions among categories in a manner that
offers an alternative to conventional approaches. His philosophy formed the
basis of Pontius and Spencer (2005), which won the Michael Brehney
prize for best paper of the year in Environment and Planning B. Pontius and Cheuk (2006) used the philosophy to derive a
cross-tabulation matrix that can analyze maps of categories where the pixels
have categorical memberships that are mixed, soft or fuzzy. That paper was the
most highly cited paper in its journal, IJGIS, during its first years of
publication. Pontius and Connors (2009) built on that paper to show how
associations among categories are sensitive to modifications in the spatial
resolution of the maps. Pontius, Peethambaram, and
Castella (2011) extended the philosophy to derive a method that compares
simultaneously three maps of mixed pixels, which is essential for the
validation of land change simulation models at multiple-resolutions. The
approach has inspired additional methods to estimate land change over time from
remotely sensed maps for the common case where map error is suspected but not
measured due to lack of ground reference information (Pontius and Li 2010,
Pontius and Lippitt 2006, Aldwaik and Pontius 2013).
Pontius, Thontteh and Chen (2008) unified the philosophy for a categorical
variable with the philosophy for a real continuous variable. Pontius and his
doctoral students are now using his philosophy to design novel methods to
construct rigorous methods for accuracy assessment of object-based
classifications. His Bachelors, Masters, and Doctoral advisees have won awards
from the Association of American Geographers more than 20 times. Pontius’
philosophy presents a new way of thinking, while his equations are elegant in
their clarity.

Pontius
spreads this philosophy in a variety of ways. He has presented it in workshops
that he has given more than 20 times since 2003 in Australia, China, Ecuador,
France, Germany, Greece, India, Japan, Mexico, Namibia, Nigeria, Russia,
Portugal, Spain, The Netherlands, and the USA. The workshop teaches the
approach in the context of land change modeling using Pontius’ model Geomod (Pontius, Cornell, and Hall
2001), which has become a standard model to predict land change especially for
management of the global carbon cycle in the context of Reduced Emissions due
to Deforestation and Degradation (REDD) projects. Pontius’ method has become
popular in part because he has designed an easy-to-use spreadsheet, which is
freely available from his web site www.clarku.edu/~rpontius.
The electronic spread sheet is especially useful for accuracy assessment in
Remote Sensing because the outputs derive from a single confusion matrix that
users enter.

Pontius presents his philosophy strategically and
theatrically to inspire a shift in the scientific culture from where scientists
previously strived to report levels of accuracy that are better than random to
where scientists now strive to report clearly the sizes of various types of
disagreement that show how maps are less than perfect. This cultural shift in
the mentality of scientists is as important as any particular quantitative
method, because the shift in mentality is necessary for clear communication
among scientists, hence is necessary for advancement in all aspects of GIS and
Remote Sensing. Pontius has induced this shift in the profession by showing how
his own maps have various types of errors, and then by demonstrating that his
work is typical of the situation of many others (Pontius et al. 2008). Pontius
designs all of his professional presentations at conferences to show these
characteristics, with the direct purpose to serve as an example to others that
it is necessary and advantageous to expose openly the disagreements among maps
and to adopt more informative methodologies that are either compliments to or
alternatives to conventional schools of thought.

He serves on the editorial boards of more than 10 journals
and has been a reviewer for more than 116 different journals. He served on the
National Research Council Committee concerning the Needs and Research
Requirements for Land-Change Modeling.